Secondary Highway 645 is a local highway that serves as an access road to Byng Inlet from Highway 529, north of Pointe-au-Baril. Highway 645 was first established in
1964, when the Byng Inlet Road was acquired by the Department of Highways of Ontario (DHO) as a new provincial highway. A Preliminary Assumption Plan was prepared by
the DHO dated December 2, 1963, which showed the proposed assumption of the Byng Inlet Road from Highway 529 westerly to Byng Inlet as a new Secondary Highway. The
plan was registered on April 1, 1964 and the new highway was formally designated as Highway 645 by an Order-in-Council, effective April 1, 1964. The highway was
gravel-surfaced at the time of designation in 1964, but a primed bituminous surface was constructed along the entire length of Highway 645 during 1967. The highway's
route has not changed since 1964. Unless posted otherwise, the speed limit on Highway 645 is 80 km/h (50 mph). There are no services available on this highway.